1. Field of the Invention
The present invention relates to an inverter apparatus configured to convert an input DC voltage into an AC voltage and output the AC voltage.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. 61-251480 discloses an AC power supply apparatus provided with two inverter circuits. The AC power supply apparatus disclosed in Japanese Unexamined Patent Application Publication No. 61-251480 produces a half-wave sine wave voltage by alternately driving the two inverter circuits, outputs a positive voltage from one of the inverter circuits, and outputs a negative voltage from the other of the inverter circuits, thereby outputting an AC voltage. In other words, the AC power supply apparatus disclosed in Japanese Unexamined Patent Application Publication No. 61-251480 produces the positive half cycles and negative half cycles of the output AC voltage by using the two inverter circuits.
In a general inverter apparatus including the AC power supply apparatus disclosed in Japanese Unexamined Patent Application Publication No. 61-251480, a smoothing capacitor is provided in the input stage (on the input side) of an inverter circuit. A current flowing through an AC load via the inverter circuits has a full-wave rectified waveform having a frequency of twice a utility power supply, whereby a ripple with the frequency described above is generated in an input voltage input to the inverter circuits. When the input voltage varies, not only does it become difficult to control the inverter circuit, but also it becomes impossible to transmit a sine wave current when the AC load is a power system (grid), thereby causing voltage waveform distortion. The smoothing capacitor is provided to suppress the ripple of an input voltage. The smaller the desired ripple of the input voltage after suppression, the higher the required capacitance of a capacitor, and hence, an electrolytic capacitor will be used, for example. However, since the lifetime of an electrolytic capacitor is short, the lifetime of an apparatus is limited. Hence, instead of using a high-capacitance capacitor, such as an electrolytic capacitor, it is desired to use a capacitor with a low capacitance, such as, for example, a film capacitor with little change over the years as a smoothing capacitor. However, when a capacitor with a low capacitance, such as a film capacitor, is used as a smoothing capacitor, a sufficient ripple suppression effect is not obtained.